An aluminum nitride sintered body includes a plurality of crystal grains and a grain boundary. Each of the plurality of crystal grains contains aluminum nitride. The grain boundary is positioned between adjacent crystal grains among the plurality of crystal grains. The average grain size of the plurality of crystal grains is from 1.5 μm to 3.0 μm. The grain boundary includes a portion in which an aluminum oxynitride containing calcium is present in an isolated state. In the aluminum nitride sintered body, the content ratio of metal elements excluding aluminum is more than 30 ppm and 300 ppm or less.